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Shellfish allergy when eating out: crustaceans vs molluscs

Published 25 October 2026

Shellfish is the word most of us say at the table. UK food law uses two others. Crustaceans and molluscs are separate entries in the 14 allergens a food business must tell you about, and fish is a third. The legal list is Annex II of assimilated Regulation (EU) No 1169/2011. The Food Standards Agency’s technical guidance, for England, Wales and Northern Ireland, and its consumer advice keep that split: crustaceans such as prawns, crabs and lobsters, then molluscs such as mussels and oysters. This page is for ordering. It does not diagnose an allergy or replace your allergy action plan. The full list is in the 14 allergens UK restaurants must declare, with guides for crustaceans, molluscs and fish.

What sits in each group

The technical guidance says the rules name no crustacean species, so every crustacean is included. Its examples are prawns, lobster, crabs, crayfish and langoustines. The guidance uses “prawns (crustaceans)”, “crayfish (crustaceans)”, “lobster (crustaceans)” and “shrimp paste (crustaceans)”. The crustacean entry adds scampi, and says shrimp paste, often used in Thai and south-east Asian curries or salads, is an ingredient to look out for. Allergy UK matches that list, and also names shrimp.

Molluscs are the other entry. The technical guidance again names no species, because the word covers them all: mussels, clams, oysters, scallops, snails, squid, cockles, winkles and octopus, including land snails. Label examples include “mussels (mollusc)”, “octopus (mollusc)” and “oyster (mollusc)”. The mollusc entry adds whelks, and says molluscs can commonly be found in oyster sauce or in fish stews. Allergy UK says a menu may call squid calamari.

Is squid shellfish?

Squid is a mollusc. A label that says “molluscs” means that group and products made from it, so a mussel allergy is the same legal line, and a prawn allergy is the other. Allergy UK describes shellfish as those two groups. “Shellfish” on its own is not a category in the list of 14. A kitchen can hear “no prawns” and still serve squid, or hear “no mussels” and still use a prawn stock. Name the group and the foods. If you need both left out, say both, and say fish if you avoid that too. How to say it is in how to tell a restaurant about your food allergy.

Sauces, crackers and shared pans

People ask if prawn crackers are safe with a shellfish allergy. A cracker sold as a prawn cracker is a crustacean question, because prawns are crustaceans. On a pack, the technical guidance expects a clear reference such as “prawns (crustaceans)”, and the consumer advice says the 14 are emphasised in the ingredients. On a plate, staff have to tell you. Brands and venues differ, so read the pack in front of you, or ask for the allergen information for the crackers that venue serves.

Shrimp paste is the crustacean the crustacean entry names in curries and salads that do not look like seafood. Oyster sauce is the mollusc the mollusc entry names, along with fish stews. “Commonly found” is the agency’s wording, so ask them to read the bottle they pour. Fish sauce is separate. Allergy UK groups it with sauces that contain fish, including ones used in casseroles and stir-fries. Ask them to read the bottle for fish, crustaceans and molluscs. XO sauce is only a menu name, not one of the 14, so ask for that bottle too. The consumer advice says allergens are less obvious in a complicated dish.

Allergy UK also names stocks and sauces, paella and fried rice, and a batter or crumb such as scampi or seafood sticks. Prawn, calamari and mussels appear together on the toppings it lists. A platter or a shared stew raises the same question about the stock. Food cooked in the same batter or oil, such as takeaway fish and chips, can expose you: fish and prawn allergens are not easily broken down by cooking and can stay in a fryer or a wok. The consumer advice says heating does not remove that potential unless the proteins are completely hydrolysed, and kitchen temperatures will not do that. There is no specific legal requirement to print “may contain”, and a missing line is not a free-from claim. Staff must give you allergen information. They need not offer another meal. The same advice says not to assume vegan food is safe if you avoid crustaceans, fish or molluscs, because vegan means no animal ingredient was used on purpose.

What to say to staff

In England, Wales and Northern Ireland, follow the consumer advice. In Scotland, follow Food Standards Scotland. Check the menu or call ahead. Be clear, give examples, and ask if they can offer a suitable meal or make one. Ask about cross-contamination from equipment, ingredients, glazes, garnishes, sauces and oils, and about a recipe change. Repeat it when you arrive. If they do not understand, ask for a manager. If you still doubt them, do not eat there. On a plate, information can be written or spoken, and if it is spoken the business must signpost where you get it.

• Are crustaceans in the dish, the sauce, the stock, the garnish or a cracker? Name prawns, shrimp paste, crab, lobster, langoustine, crayfish and scampi.
• Are molluscs in it? Name mussels, oyster sauce, clams, scallops, squid or calamari, octopus, snails and whelks.
• Is fish in it as well, including fish sauce?
• Will this share a stock, a paella, a stew, a platter, a fryer, a wok or a batter with the other group?
• If there is a bottle or a pack, does it emphasise crustaceans or molluscs?

One allergy does not decide the other

A prawn allergy does not, by itself, mean you will react to mussels. A mussel allergy does not, by itself, mean you will react to prawns. This page cannot choose your foods. The NHS page on food allergy lists shellfish, with prawns, crab and lobster as the examples, among foods that commonly cause a reaction, and says you can be allergic to any food. See a GP if you think you or your child may have a food allergy. You may be referred for tests, and your specialist will give you an allergy action plan. Follow that plan.

Allergy UK says that if you are allergic to one type of shellfish or fish, it is safer to avoid all types when you eat out, because of cross-contact. That is about shared kitchens. It is not your test result. If your plan names one group, use that legal name, and still ask about the oil and the stock. If it names both, say both before the food is cooked.

If someone reacts

If you think someone is having anaphylaxis, follow the NHS. Anaphylaxis is a life-threatening allergic reaction that happens very quickly. Use an adrenaline auto-injector if they have one, even if the symptoms are mild. The instructions are on the side of the injector. Call 999 and say you think it is an anaphylactic reaction. Lie down and do not stand or walk, even if they feel better. You can raise the legs, sit up slowly if breathing is difficult, and lie on the left side in pregnancy. If symptoms have not improved after 5 minutes, use a second injector. The NHS food allergy page says to use a prescribed adrenaline auto-injector or nasal spray straight away in a serious reaction, then call 999 even if the person seems better. Restaurant steps are in what to do in an allergic reaction. If this differs from the NHS, follow the NHS and that person’s plan.

Where this sits on SafePlate

You can search for restaurants for a food allergy with crustaceans, molluscs, fish, or any mix of them, and you can search on the SafePlate homepage. Searching SafePlate is free. Unknown means no menu or visitor note mentions that food. You still ask. Bristol and Glasgow explain who handles food law locally. They do not name a kitchen as safe.

The usable allergy chef card, in 38 languages, is part of SafePlate Plus. Plus fills it from your profile so you can show it or print it. The allergy chef card page is a preview unless you have Plus. You cannot fill that sample in, hand it over as yours, or print it. If you avoid both groups, put them on separate lines.

Set up your foods before you search. This is not medical advice. Confirm the meal with the kitchen. In the UK, if you think someone is having anaphylaxis, call 999.